No Relation Between Short-term Sodium Intake And Whole Body Sweat Sodium Concentration During Exercise-heat Stress

Context:There is interest in including recommendations for the replacement of the sodium lost in sweat in individualized hydration plans for athletes.Purpose:Although the regional absorbent-patch method provides a practical approach to measuring sweat sodium losses in field conditions, there is a need to understand the variability of estimates associated with this technique.Methods:Sweat samples were collected from the forearms, chest, scapula, and thigh of 12 cyclists during 2 standardized cycling time trials in the heat and 2 in temperate conditions. Single measure analysis of sodium concentration was conducted immediately by ion-selective electrodes (ISE). A subset of 30 samples was frozen for reanalysis of sodium concentration using ISE, flame photometry (FP), and conductivity (SC).Results:Sweat samples collected in hot conditions produced higher sweat sodium concentrations than those from the temperate environment (P= .0032). A significant difference (P= .0048) in estimates of sweat sodium concentration was evident when calculated from the forearm average (mean ± 95% CL; 64 ± 12 mmol/L) compared with using a 4-site equation (70 ± 12 mmol/L). There was a high correlation between the values produced using different analytical techniques (r2= .95), but mean values were different between treatments (frozen FP, frozen SC > immediate ISE > frozen ISE;P< .0001).Conclusion:Whole-body sweat sodium concentration estimates differed depending on the number of sites included in the calculation. Environmental testing conditions should be considered in the interpretation of results. The impact of sample freezing and subsequent analytical technique was small but statistically significant. Nevertheless, when undertaken using a standardized protocol, the regional absorbent-patch method appears to be a relatively robust field test.

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Relation between Regional and Whole Body Sweat Sodium Concentration and the Effect of Exercise Intensity

Medicine & Science in Sports & Exercise ◽

10.1249/01.mss.0000537132.67188.d9 ◽

2018 ◽

Vol 50 (5S) ◽

pp. 620

Author(s):

Lindsay B. Baker ◽

Corey T. Ungaro ◽

Bridget C. Sopeña ◽

Ryan P. Nuccio ◽

Adam J. Reimel ◽

...

Keyword(s):

Exercise Intensity ◽

Sodium Concentration ◽

Whole Body ◽

Sweat Sodium Concentration ◽

Sweat Sodium

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Hydration Status, Fluid Intake, Sweat Rate, and Sweat Sodium Concentration in Recreational Tropical Native Runners

Nutrients ◽

10.3390/nu13041374 ◽

2021 ◽

Vol 13 (4) ◽

pp. 1374

Author(s):

Juthamard Surapongchai ◽

Vitoon Saengsirisuwan ◽

Ian Rollo ◽

Rebecca K. Randell ◽

Kanpiraya Nithitsuttibuta ◽

...

Keyword(s):

Fluid Intake ◽

Sweat Rate ◽

Statistical Significance ◽

Sodium Concentration ◽

Fluid Replacement ◽

Whole Body ◽

Hydration Status ◽

P Value ◽

Sweat Sodium Concentration ◽

Sweat Sodium

Aim: The purpose of this study was to evaluate hydration status, fluid intake, sweat rate, and sweat sodium concentration in recreational tropical native runners. Methods: A total of 102 males and 64 females participated in this study. Participants ran at their self-selected pace for 30–100 min. Age, environmental conditions, running profiles, sweat rates, and sweat sodium data were recorded. Differences in age, running duration, distance and pace, and physiological changes between sexes were analysed. A p-value cut-off of 0.05 depicted statistical significance. Results: Males had lower relative fluid intake (6 ± 6 vs. 8 ± 7 mL·kg−1·h−1, p < 0.05) and greater relative fluid balance deficit (−13 ± 8 mL·kg−1·h−1 vs. −8 ± 7 mL·kg−1·h−1, p < 0.05) than females. Males had higher whole-body sweat rates (1.3 ± 0.5 L·h−1 vs. 0.9 ± 0.3 L·h−1, p < 0.05) than females. Mean rates of sweat sodium loss (54 ± 27 vs. 39 ± 22 mmol·h−1) were higher in males than females (p < 0.05). Conclusions: The sweat profile and composition in tropical native runners are similar to reported values in the literature. The current fluid replacement guidelines pertaining to volume and electrolyte replacement are applicable to tropical native runners.

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Relationship of osmotic inhibition in thermoregulatory responses and sweat sodium concentration in humans

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.2001.280.3.r623 ◽

2001 ◽

Vol 280 (3) ◽

pp. R623-R629 ◽

Cited By ~ 37

Author(s):

Akira Takamata ◽

Tetsuya Yoshida ◽

Naoko Nishida ◽

Taketoshi Morimoto

Keyword(s):

Heat Stress ◽

Plasma Osmolality ◽

Sodium Concentration ◽

Inhibitory Effect ◽

Body Core Temperature ◽

Heat Acclimatization ◽

Thermoregulatory Responses ◽

Unit Increase ◽

Sweat Sodium Concentration ◽

Sweat Sodium

Heat acclimatization improves thermoregulatory responses to heat stress and decreases sweat sodium concentration ([Na+]sweat). The reduced [Na+]sweat results in a larger increase in plasma osmolality (Posmol) at a given amount of sweat output. The increase in Posmol inhibits thermoregulatory responses to increased body core temperature. Therefore, we hypothesized that the inhibitory effect of plasma hyperosmolality on the thermoregulatory responses to heat stress should be attenuated with the reduction of [Na+]sweat due to heat acclimatization. Eleven subjects (9 male and 2 female) were passively heated by immersing their lower legs into water at 42°C (room temperature 28°C and relative humidity 30%) for 50 min following isotonic or hypertonic saline infusion. We determined the increase in the esophageal temperature (Tes) required to elicit sweating and cutaneous vasodilation (CVD) (ΔTes thresholds for sweating and CVD, respectively) in each condition and calculated the elevation of the Tes thresholds per unit increase in Posmol as the osmotic inhibition of sweating and CVD. The osmotic shift in the ΔTes thresholds for both sweating and CVD correlated linearly with [Na+]sweat( r = 0.858 and r = 0.628, respectively). Thus subjects with a lower [Na+]sweat showed a smaller osmotic elevation of the ΔTes thresholds for sweating and CVD. These results suggest the possibility that heat acclimatization attenuates osmotic inhibition of thermoregulatory responses as well as reducing [Na+]sweat.

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